I. Field of the Invention
This invention relates to a non-pneumatic tire and a method for producing a non-pneumatic tire and, more particularly, to a non-pneumatic tire having an elastomeric hoop and a method for producing a non-pneumatic tire formed from at least two different materials and having an elastomeric hoop.
II. Description of the Related Art
A great deal of work has been done to develop a non-pneumatic tire that has the same performance characteristics as a pneumatic tire. Pneumatic tires are geometrically torus shaped and are distinguishable from non-pneumatic tires in that they have a flexible membrane pressure container. This pressure container when filled with air under appropriate pressure allows the tire to meet a variety of performance characteristics. These characteristics include load carrying capacity, rolling resistance, cushioning ability, noise and vibration reduction and road handling ability.
By definition, pneumatic tires contain pressurized air within a hollow chamber. While there have been many improvements to these tires, one of the greatest disadvantages is that of flat tires and blowouts. Therefore, a great deal of research has gone into producing a pneumatic tire having a run-flat capability. Improvements in this area have allowed tire designers to develop pneumatic tires that are able to adequately perform without pressurized air. Typically, this performance permits the tire, while un-inflated, to adequately operate over a certain distance and for a certain time. This eliminates the need to change the tire immediately. Other improvements have dealt with flat tires that seal themselves when a hole or puncture is acquired, such as driving over a sharp object. These designs place a type of liquid material within the tire, that, upon puncture of the tire, flows to the area surrounding the newly formed hole thereby preventing the air from escaping. In all known cases, overcoming flats and/or blowouts in pneumatic tires has come at the expense of performance characteristics.
Non-pneumatic tires eliminate the problem of a flat and/or blowout by eliminating the need for pressurized air. Non-pneumatic tires are typically solid tires or foam tires or a combination thereof, having no hollow chambers therein. Thus, the inherent problems within pneumatic tires discussed above are eliminated. However, many of the performance characteristics found with pneumatic tires have not been duplicated in non-pneumatic tires. In particular, the performance characteristics of cushioning ability, rollability, noise and vibration reductions have not been equaled. Thus, the pneumatic tire is the standard in virtually all passenger tire and wheel applications and, more specifically, automobiles, trucks, vans, bicycles, carts, etc.
Initially, non-pneumatic tires were made of natural rubber. As the technology has developed, various other materials have been used. These other materials have greater performance characteristics than rubber. Most of these materials have come from the polymer industry. For example, bicycle tires have been made of polyurethane foam. As the polymer industry has developed, it has long been desired to replicate the characteristics of a pneumatic tire by using polymers.
The polymer-based tires, such as polyurethane foam, are manufactured by a molding process. The mold is filled with the polyurethane foam, or like material, while under pressure. The pressure xe2x80x9cpushesxe2x80x9d the foam into the cavital areas of the mold.
A typical method of producing non-pneumatic bicycle tires is known as spin casting. This method involves filling the mold with a pre-blended polymer material while the mold is rotated about its axis. The rotation of the mold produces a centrifugal force effecting movement of the material radially outwardly. The material thus collects in the form of an annulus within the mold. The rotation of the mold continues until the material has gelled sufficiently. The mold is thereafter stopped from rotation and the material is allowed to fully cure.
The known prior art methods of producing a non-pneumatic tire have comprised a single polymer-based tire. Certain polymers may provide distinct advantages in some properties as compared to other polymers. For example, one polymer may exhibit superior vibration and noise characteristics in comparison to another polymer, however, its load-carrying capacity may be inferior. There exists a problem in art to provide a non-pneumatic tire having performance characteristics similar to a pneumatic tire without the disadvantages such as flats and blowouts. Ideally, the improved tire would utilize a variety of polymeric materials in order to maximize the performance.
In the automobile tire industry, it has been found that providing belts within a pneumatic tire structure allows the tire to function as a fixed circumference hoop, meaning that the circumference is the same whatever shape the tire assumes, be it circular, elliptical, or semi-elliptical. The belts provide high planar rigidity which stiffens the tire in order to hold the tread surface flat against the road. In other words, the footprint of the tire is elongated and stabilized.
Heretofore, the belt technology commonly found in the automotive tire industry has not been applied to bicycle tires because of the impracticality of adding belts, for instance steel, to bicycle tires. However, the present invention provides an alternate technology which achieves many of the benefits of a belted tire structure.
The present invention contemplates a new and improved non-pneumatic tire having an elastomeric hoop and a method of manufacturing non-pneumatic tires made of at least two different materials which is simple in design, effective in use, and overcomes the foregoing difficulties and others while providing better and more advantageous overall results.
In accordance with the present invention, a non-pneumatic tire is provided for attachment to an associated wheel rim. The non-pneumatic tire comprises a first annular portion including a tread surface formed of a first material, and a second annular portion formed of a second material and disposed radially inwardly of the first annular portion.
According to one aspect of the invention, the first material comprises elastomeric material, and the second material comprises foamed material.
According to another aspect of the invention, the first annular portion has a density of 55-65 lb/ft3 and the second annular portion has a density of 20-35 lb/ft3.
According to another aspect of the invention, the second annular portion comprises greater than 60% closed cellular structure.
According to another aspect of the invention, the elastomeric material is a product of a reaction of isocyanate and polyol mixture and the foamed material is a product of a reaction of isocyanate, a polyol mixture, and a blowing agent.
According to another aspect of the invention, the first annular portion includes an outer annular region encompassing the tread surface and an inner annular region. A predetermined physical characteristic of the outer annular region and the inner annular region are different.
According to another aspect of the invention, the predetermined physical characteristic is Shore A hardness. The Shore A hardness of the outer annular region is less than the Shore A hardness of the inner annular region.
According to another aspect of the invention, the Shore A hardness of the outer annular region is 45-65 and the Shore A hardness of the inner annular region is 60-80.
According to another aspect of the invention, the predetermined physical characteristic is tensile modulus. The tensile modulus of the outer annular region is lower than the tensile modulus of the inner annular region.
According to another aspect of the invention, the inner annular region is chemically bonded to the outer annular region at an interface thereof.
According to another aspect of the invention, inner annular region is adhesively bonded to the outer annular region at an interface thereof.
According to another aspect of the invention, the first annular portion further includes an intermediate annular region between the outer and inner annular regions.
According to another aspect of the invention, the hardness of the intermediate region is different than the hardness of the inner annular region.
According to another aspect of the invention, a non-pneumatic tire for attachment to an associated wheel rim is provided. The non-pneumatic tire comprises a first annular portion including a tread surface formed of elastomeric material and including an outer annular region encompassing said tread surface and an inner annular region. The outer annular region exhibits a Shore A hardness of 45-65 and the inner annular region exhibits an Shore A hardness of 60-80. A second annular portion disposed radially inwardly of said first annular portion is formed of foamed material and exhibits a Shore O value of 35-55.
One advantage of the present invention is that the elastomeric material disposed behind the tread region acts as an xe2x80x9celastomeric hoopxe2x80x9d to impart favorable ride characteristics to the non-pneumatic tire.
Another advantage of the present invention is that the footprint length, width and rolling resistance of the tire may be controlled by use of the hoop.
Another advantage of the present invention is that the compliance, force transfers characteristics and weight of the non-pneumatic tire may be controlled by the properties of the foamed material.
Another advantage of the present invention is that the presence of more than one hoop allows each hoop to exhibit different hardness characteristics and thereby improve tire performance.
Still other benefits and advantages of the invention will become apparent to those skilled in the art upon a reading and understanding of the following detailed specification.